I’ve sent the Chinese uSDX QRP SDR Transceiver back…

A couple weeks ago, I posted my initial thoughts about the Chinese uSDX/uSDR QRP transceiver.

In short, it wasn’t exactly a glowing review.

I’ve now tested the uSDX at home for a couple weeks and decided to send it back to the eBay distributor.

I made a short video detailing the reasons why I’m sending it back (see blow), but in short there are two main reasons:

1.) The receiver and audio

I understand that quality control varies greatly with the various versions of the uSDX being manufactured in China.

With that in mind, I have to assume mine is one with an incredibly inadequate receiver.

My uSDX receiver overloaded when in the presence of pretty much any strong-ish signal.

As an example, one of the first signals I tuned to on the CW portion of the 20M band–K4NYM activating a park in Florida–had FT8 audio bleeding in from over 20 or 30 kHz away. K4NYM had an S9 signal, but he was very much a portable operator, not a blowtorch contest station. The uSDX should have easily been able to handle this situation.

On my unit, if you tuned to a strong CW signal (or worse yet, a pileup) it opened the receiver window so wide that signals across the band bled through. There was essentially no selectivity.

I quickly learned that I couldn’t trust this uSDX unit during a park or especially a summit activation. If I had the good fortune of attracting a small pileup in the field, I knew the receiver would fall apart and it would be a real struggle to work anyone.  I tried altering some of the uSDX settings, but nothing helped.

On top of that, the audio amplification chain produced a lot of unwanted hash and splatter.

Even when the audio was turned to “0” you could still hear splatter from receiver overload punching through the speaker. It was ever-present.

To be clear, I’m not terribly picky about audio in field transceivers. I don’t expect contest-grade performance in this class of radio. But the audio needs to have enough positive characteristics that it’s functional. I believe my uSDX unit pushed those boundaries too far.

It’s no exaggeration to say that it had the least refined audio of any QRP transceiver I’ve ever tested.  It was fatiguing to listen to this uSDX unit for any meaningful length of time.

The transmitted signal

Even if this uSDX had an adequate receiver, I would have still sent it back due to its transmitted signal.

As I reported earlier, I took the uSDX to my buddy Vlado (N3CZ) who hooked it up to his service monitor. We discovered (with little surprise) that the transmitted signal wasn’t exactly clean. I’d read in advance that some Chinese uSDX units produce a signal that likely falls below FCC signal purity standards and I now suspect this unit is either very close to or exceeds that threshold.

We didn’t want to count on the measurements from this older service monitor because it had been some time since its last calibration and there was a slight issue with the BNC input. Still, we repeated the test numerous times across the bands and the average showed consistency in results. The uSDX produced spurs on harmonics and noise in the signal.

The noise was especially noticeable when compared to that of my Elecraft KX2 which we also tested.

I’ve been contacted by other Chinese version uSDX owners who found their unit had a fairly clean transmitted signal. I’ve also read numerous reports from owners who tested their unit to find that it didn’t meet FCC specs.

I assume quality must vary greatly from unit to unit.

I like knowing I’m a good neighbor on the HF bands, so I simply couldn’t live with the signal this uSDX produced and I had no desire to attempt to modify it because of the receiver issues mentioned above. It just wasn’t worth my time.


I made this quick unscripted video only moments before shipping the uSDX back:

Click here to watch on YouTube.

Reminder: This is not the uSDX Open Source Project

I’ve been careful to note that my unit is a Chinese version of the uSDX transceiver.

In case you are unfamiliar, the uSDX is an SDR transceiver that was originally developed on the hardware of the original QCX by Guido (PE1NNZ). Manuel (DL2MAN) also worked on this project and encouraged more interest and the uSDX spun off into its own separate project, with its own discussion group.

As Hans (G0UPL) notes:

[These Chinese uSDX transceivers] aren’t “clones” because uSDX is open source and any productions of the radio by anyone are legitimate. Having said that, you may question what quality and support you will get.

[…]The uSDX, and particularly its eBay implementations, are not a high performance transceiver.

[…]The eBay implementations also often suffer inferior components and poor design choices which are not compatible with the original uSDX design. 

As Hans implies, the homebrew/open-source version of the uSDX–for those who have built them–performs much better than the Chinese versions.

Still, at time of publishing this post, I know of no complete uSDX kit that can be purchased [please correct me if I’m wrong about this] so builders would need to source all of the components on their own. This could get pricey for those of use who don’t have a large inventory of parts.

The Chinese uSDX transceivers are appealing because they’re so darn accessible.

My advice? Skip the Chinese uSDX

Obviously, I can’t recommend the Chinese version of the uSDX.

I’m sure there are better examples of the Chinese uSDX out there on the market–ones that might be worth keeping. But I have to admit: at time of posting (December 20, 2021), I suspect “good” Chinese uSDX models are the exception, not the rule.

My advice would be that if you decide to purchase a Chinese version of the uSDX:

  • Please test its transmitted signal before hopping on the air.
  • Purchase it from a retailer with the highest customer feedback points in case you experience an issue.
  • If you have the skill and desire, plan on modifying it to tweak performance.

If you own the Chinese uSDX, please comment with your own thoughts and experience. Again, I’m not claiming all versions will have the dismal performance of the unit I purchased, but I think there is a reasonable probability.

13 thoughts on “I’ve sent the Chinese uSDX QRP SDR Transceiver back…”

  1. Stephen, G7VFY, notes that he did warn you about this radio, Thomas, but, on the other hand, you do provide a valuable service for many other hams who might consider purchasing this radio. I used to read a column in Byte magazine, and later online, by the late Jerry Pournelle called “Computing at Chaos Manor, in which he described his experiences, mostly problematic, with computer software and hardware. He used to say that he tried these things so that we (his readers) didn’t have to. Thanks for serving the ham community in like fashion.

    Bill, W8BC

  2. I am thrilled that I had 2 orders canceled by the sellers back in September. My guardian angels prevented me from getting one of these dogs. And to be honest, this isn’t the first review that absolutely slaughtered the quality and workmanship of these.

    With that, I took my money, and bought a QRP Labs QCX Mini for 40m. It’s bombproof by comparison.


    John KB2HSH

  3. I bought one of the uSDX rigs, the smaller 4d x 3w x 1h with similar display. I did a test of the rig also. I paid $115 at AliExpress.

    I was pleased with what I got. I cannot see why someone paying $115 or even $160 as some charge expect a radio that is of the quality of like a KX2/3 or other QRP rig. How many Hams have UV5R HTs, they are dirty, but so many use them for they do work well.

    With your test Steve, you did not state the scale on the Service Monitor, the IFR1200S (I have one also although their spectrum analyzers are not all that great, I use my Rigol 815TG). If the scale is 10db per div the photo shows the spurious emissions are down 40db, more than FCC spec for HF.

    My uSDX did work, I used for a few contacts. Yes the audio overloaded, but I put up with it. The rcvr in mine was not very sensitive, 1uV. Xmt power dropped off on upper bands, was about 5W on 80 & 40m, but at 10m was down to 2.4W.

    I was pleased with the rcvr, it worked, selectivity was good with the tunable IF filters. Not direct sampling. I dont do pile ups, dont waist my time and for QRP trying to compete with 100W base stations, just move on.

    I disagree with one not taking this into the field. I would do it with no issue. I work only CW. Although I copy code myself I did find the CW decoder in my rig to work rather well. Would be useful for someone learning CW.

    These rigs are not what one would expect compared to a $500-1000 QRP rig, why would anyone expect it, but does work and has some good feature.

    These uSDX rigs are good for someone just wanting to get into QRP. As we all know who have been doing QRP for a time know it takes paticence and work. Some might spend $500 and find not what they want to do. So one of these less expensive rigs is good way to try it without breaking the bank.

    73, ron, n9ee/r

    1. I strongly disagree that this is a good intro to working QRP. Using second rate equipment is never enjoyable and doesn’t make for a positive experience.

  4. My broke down less than 3 days after it arrived. The audio just went into motor boating. Tx seems still ok but only CW. It’s junk. They did offer me a refund of 42 euros but I couldn’t be bothered. Sent it back and got my money and postage refunded.

    1. Tu crois vraiment que tu vas pousser un rédacteur bénévole à te faire une rédaction en français alors que 99.9% des radioamateurs parlent en anglais ? 🙂

      Qui es tu pour le mériter ? Je pense qu’il fallait aller à l’école au bon moment :3

  5. @Ron N9EE, just be serious if you really need to start QRP you can find great second hand FT817 TRX with a very decent price. Yours is working well as you said but think about those who purchase a defective product and i can tell you there is a lot . Due to obvious quality fading buying this product is a total waste of money since you are not sure at all your product will perform decently . Your post post is just encouraging people to buy a most probably defective product.

    1. I agree 110% with F5NPV. BESIDES the battle-tested 817 (that has been in production for 20 years and is arguably the most popular piece of amateur radio gear ever), there are many other affordable radios that can be had for peanuts. I bought a semi-completed Ramsey QRP40 for $3 this summer, and a Pacific Antennas Easy RX for $25. They make a great portable set up that you wouldn’t care too much about if they were broken or similar.
      These Chinese radios are a great idea, but in practice they aren’t worth it even if they were 1/4 of the price.

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